Rat incisor dentin was studied by polarizing light microscopy, light microscopy, fluorescence microscopy and scanning electron microscopy to investigate the structural differences between labial and lingual dentin. In lingual dentin, crystals and collagen fibers were regularly arranged, the axis of orientation being parallel to the long axis of the incisor and perpendicular to the dentinal tubules. The crystals appeared to be arranged with inotropic calcification parallel to the long axis of the collagen fibers. In contrast, in labial dentin, crystals and collagen fibers were arranged irregularly, and the crystals showed radial orientation with spheritic calcification. These differences in the crystal and collagen fiber orientation in lingual and labial dentin may possibly arise from different patterns of calcification.
Correlation coefficients between tooth crown and root measurements and among root measurements in an individual dentition were calculated in order to determine the difference in variability between tooth crown and root dimensions. Root lengths were highly correlated with each other not only within the upper or lower dentition, but also between the upper and lower dentition. Total heights of both upper and lower dentitions had significant correlation coefficients with almost all the crown heights, but not so many with buccolingual and mesiodistal diameters. These facts indicated a high variability of root length. However, high correlations within root lengths suggested their invariabilities within an individual dentition.
The purpose of this study was to investigate the changes in taste sensitivity during aging using four standard taste solutions. The subjects consisted of 50 normal volunteers who were divided into two groups. The younger age group was composed of 27 individuals between the ages of 20 and 30 years. The older group consisted of 23 individuals between the ages of 50 and 77 years. In order to evaluate the anatomic form of the fungiform papillae, close-up photographs (×3) were taken on the right side of the tongue in all subjects. Then, each subject's taste threshold was measured by placing the four taste solutions on the following structures : fungiform papillae, circumvallate papillae and soft palate. The anatomical forms of the fungiform papillae were significantly different upon comparison of the two groups (p <0.05), and the taste sensitivity of fungiform and circumvallate papillae also showed significant differences (p <0.05).
The present studies were aimed at the development of monomers for dental resins, for which the authors substituted the 8 Cl atoms in P4N4Cl8 with hydrophobic groups (Ph, TF and OF) and a polymerizing group (EMA), and bulk-polymerized them in order to examine their physical properties. Attention was focused on the relationship between the number of substituted hydrophobic groups and the mechanical properties, thermal expansion coefficient, polymerization shrinkage, contact angle, refractive index, water sorption and solubility to establish a basis for the practical use of cyclophosphazene monomers as dental resin monomers. The results obtained were as follows : compressive strength, transverse strength and hardness under dry conditions decreased in accordance with the increased number of substituted hydrophobic groups, but their degree of decrease in mechanical strength under wet conditions (after immersion in water) was small, proving that in comparison with PNC-EMA 4006, having no hydrophobic group, the mechanical properties under wet conditions were improved. It was found that by hydrophobic group substitution, contact angle increased and water sorption decreased. On the other hand, thermal expansion coefficient increased in accordance with the number of substituted hydrophobic groups, but polymerization shrinkage in all cases was very small, 3.09-9.08 vol%. Solubility also showed low values, 0.053 0.160 wt% when the number of substituted hydrophobic groups was 1-2.
In this study, the functional forces acting on maxillary complete dentures during mastication and swallowing were determined from three different locations by means of strain gauges. It was found that the functional forces caused by swallowing are quite marked in themselves and can cause deformation of the denture base resulting in undesirable force on the denture-bearing tissues.